A variety of air humidifying processes and air humidifying devices are known which have different operating principles. Thus for example an air humidifying process is known from U.S. Pat. No. 4,269,087 in which air bubbles through a container that is partially filled with water and is saturated with water vapour in this process. The desired relative humidity is adjusted by admixing dry air wherein a humidity sensor is used to monitor the relative humidity.
Another air humidifying process is known from U.S. Pat. No. 5,669,554 in which air bubbles through a heated bottle that is partially filled with water during which it is saturated with water vapour. At higher air flow rates, the humidification is doubtful because larger air bubbles can be formed in the water whose saturation is no longer ensured. It is difficult to set uniform low working pressures in the range of a few 10 mbar since the pressure of humid air is also influenced by the hydrostatic pressure of the water column in the bottle and there can be large fluctuations in the pressure when the formation of air bubbles is irregular. In such processes in which air is passed through water filled into a container, one usually has to take care to avoid microbial contamination of the water store in the relevant container.
An air humidification process is known from U.S. Pat. No. 5,394,734 in which atomized water is sprayed by means of a nozzle into a space to be humidified. The amount of water to be atomized has to be controlled using a humidity sensor to monitor the relative humidity in the relevant space.
A corrosion chamber where humidity is generated by atomizing water is known from U.S. Pat. No. 5,988,003. In this case it is critical that the temperature and the humidity in the chamber have to be controlled simultaneously and depend on one another. The amount of water to be atomized is controlled which requires a humidity sensor to monitor the humidity.
It is known from U.S. Pat. No. 5,231,029 that humid air of about 95% relative humidity can be used to prevent sample carriers from drying out in an incubator. More details on the generation of the humid air are not given in U.S. Pat. No. 5,231,029.
Humidity generators have also already been proposed in which air bubbles through water in a thermostatic container and is saturated with moisture in this process. The targeted relative humidity below the saturation point is produced by isothermal expansion of the saturated vapour. In such humidity generators it is difficult to set uniform low working pressures in the range of a few 10 mbar since the hydrostatic pressure of the water column that is dependent on the filling height of the water in the container is added to the desired working pressure. Moreover, there is a large fluctuation in the pressure due to irregular formation of air bubbles when the water is passed through the water column.
In the previously known humidification processes it is difficult to simultaneously maintain a defined humidity, a defined temperature and a defined pressure or air flow or to adjust these parameters substantially independently of one another. In the humidification processes using humidity sensors there is the problem that the humidity sensors are generally inaccurate at relative humidities above 90% especially when dew forms. Humidification processes in which air is passed through water containers in order to saturate the air with water vapour, have the disadvantage that there is a risk of contamination of the water containers by microbes or algae. When the air flow is higher, larger air bubbles are usually formed in the water whose saturation with moisture cannot be ensured. Moreover, it is difficult to maintain small working pressures for the already mentioned reasons.